Magnetic Field Sensing Device

This application claims priority to, and the benefit of, Belgium Application No. 2022/5385 (“Magnetic field sensing device”), filed on May 19, 2022, the entire contents of which are incorporated herein by reference.

The invention relates to the field of devices and methods for sensing magnetic field distributions.

Devices for measuring the magnetic field distributions of any permanent magnet and magnet assemblies are known in the art. Such devices are referred to as magnetic field sensing devices, sometimes also referred to as magnetic field cameras, and are composed of multiple magnetic field sensing elements to allow localized measurements enabling e.g. to determine the spatial distribution of the magnetic field in the area sensed by the magnetic field sensing device with appropriate resolution. These magnetic field sensing elements may be arranged in 1-dimensional or 2-dimensial arrays in the form of a matrix or grid.

An example of such magnetic field sensing device is disclosed in EP1720026A1. The magnetic field sensing elements used are Hall sensors arranged in the form of a matrix. To enable individually addressing each of the Hall sensors in the matrix switches are used in the form of transistors. Hall sensors and switches are made of a semiconductive material.

In recent years approaches for measuring magnetic fields using diamond Nitrogen Vacancy (NV) center materials have been studied. For examples Bourgeois, E., Jarmola, A., Siyushev, P. et al. Photoelectric detection of electron spin resonance of nitrogen-vacancy centres in diamond. Nat Commun 6, 8577 (2015) describes two such approaches: Optical Detection of Magnetic Resonance (ODMR) and Photocurrent Detection of Magnetic Resonance (PDMR).

Existing magnetic field sensing devices composed of Hall sensors and transistor switches made of a semiconductive material have their merits for measuring magnetic field distributions.

U.S. Pat. No. 10,901,054B1 discloses an integrated optical waveguide and electronic using quantum defect centers. Like many current designs, the pair of electrodes therein are arranged opposite to each other in a more or less symmetrical manner. However, such arrangement results in generating a non uniform electrical field, in particular at the ends. Therefore, the magnetic fields of adjacent sensing devices may interfere with each other and result in inaccurate results.

It is however an aim of the present invention to provide an alternative magnetic field sensing device and method to make the measuring result more accurate.

It is a further aim of the present invention to integrate such magnetic field sensing device on a diamond NV center substrate to obtain a higher spatial resolution of the magnetic field sensing element and to improve measurement sensitivity and overall measurement time.

To achieve these aims in an aspect of the present invention a magnetic field sensing device for determining the magnetic field distribution in an area has been provided, comprising a predetermined area of a diamond NV center substrate and a controller. The predetermined area has a plurality of magnetic sensing elements, each of said plurality of sensing elements has a first contact and a second contact electrically contacting a surface of the diamond NV center substrate. Each second contact is electrically isolated from each first contact.

The diamond NV center substrate may constitute a diamond material containing Nitrogen Vacancy (NV) centers in the form of a thin plate.

In accordance with the invention, the controller is configured to control

The measurement unit typically comprises an amplifier, equipment for measuring a current and/or voltage, signal processing means and a data processing unit.

To enable a magnetic sensing element to sense a magnetic field simultaneously a local electrical field is to be generated by applying a bias voltage between the first and second contact of the sensing element, the sensing element must be exposed to light of a predetermined wavelength or wavelength range, and the magnetic element is to be irradiated with microwaves of a predetermined frequency or frequency range. The combined presence of the local electrical field and the exposure to light induces and enables collection of a photocurrent. Simultaneously irradiating with microwaves influences the photocurrent dependent on the presence of a magnetic field. Hence by electrically connecting the second contact of the sensing element to a measurement unit sensed magnetic field values can be extracted by the measurement unit from the photocurrent detected by the second contact. The above can be repeated for each sensing element in order to sequentially obtain the magnetic field contributions of each individual sensing element or can be done in parallel for selected magnetic sensing elements by connecting the second contact of each selected magnetic sensing element separately to a measurement unit. The capability to extract sensed magnetic field values for each individual magnetic sensing element, so called read-out selectivity, can be achieved in several ways without the need to connect each second contact separately. Non-selected magnetic sensing elements that have no local external field applied and/or are not exposed to light do not generate a photocurrent. Hence if their second conductive line is connected to the second contact of a selected magnetic sensing element read-out selectivity of the selected magnetic sensing element is not affected. Spatially controlling the light sources and the electrical fields creates design-freedom allowing for less complex design and faster and more accurate measurements. When grouping second contacts read-out selectivity can also be accomplished by modulating the bias voltage and/or the light source and/or the microwave source such as to expose different magnetic sensing elements or groups thereof to signals with different modulation frequencies allowing to separate the contribution of individuals magnetic sensing elements to the photocurrent detected by the grouped second contacts using a multifrequency lock-in amplifier.

In an embodiment of the invention either one of the first and second contact of the magnetic sensing element is located inward to the other one of the first and second contact. In particular, the arrangement may be such that one of the first and second contact of a magnetic sensing element substantially surrounds the other one of the first and second contact, i.e the two contacts have different shapes, and one extends around the other (along a closed line or only partially). For example one contact is a spot (of any shape) located at the centre of the sensing element while the other contact is a line arranged towards the periphery of the sensing element. Doing so contributes in defining the substrate area (between the two contacts) to which an electrical field is applied as well as the uniformity of the electrical field in the magnetic sensing element. Moreover, it also improves shielding a magnetic sensing element from influencing by neighbouring magnetic sensing elements.

The plurality of sensing elements may be arranged in a 1D or 2D array such as to define a matrix or grid of magnetic sensing elements forming the magnetic sensing device. First parallel conductive lines oriented in a first direction may be provided to connect the first contacts and second parallel conductive lines oriented in a second direction may be provided to connect the second contacts. This allows to connect the first and second contacts of rows and/or columns of magnetic sensing elements in the matrix.

The first direction can be chosen perpendicular to the second direction. Hence the first conductive lines may connect the first contacts of rows of magnetic sensing elements while the second conductive lines may connect the second contacts of columns of magnetic sensing elements, or vice versa. This is convenient as the first and second conductive lines can easily be accessed at different sides of the magnetic sensing device. A multiplexer may be provided to which all the second conductive lines are connected while the output of the multiplexer is connected to the measurement unit. Thereby all the second contacts are connected and they can be read out by the measurement unit in rows or columns. For example, assume the first conductive lines connect rows of magnetic sensing elements and the second conductive lines, i.e. the read-out lines, connects columns of magnetic sensing elements and that a single row of magnetic sensing elements is selected and biased such that an electrical field is present in each sensing element of that row. When simultaneously this row of sensing elements is exposed to light at a predetermined wavelength and irradiated with microwaves at a predetermined frequency then in each sensing element of that row a photocurrent is generated influenced by the magnetic field to the extent present. In such case each column has only one active sensing element, or in other words each read-out line addresses a single active sensing element. Hence from the photocurrent measured by the measurement unit, as the read-out lines are selectively connected to the measurement unit by the multiplexer, the sensed magnetic field values of a single magnetic sensing cell can be extracted.

In an embodiment of the invention, when the biasing element is controlled to bias the first contacts of the selected sensing elements, the biasing element may be further controlled to connect the first contacts of the non-selected sensing elements to ground. As the second contacts are all grounded this suppresses potential noise picked up by the second contacts of non-selected sensing elements which could potentially affect the reliability and accuracy of the photocurrent measured and by consequence also the reliability and accuracy of sensed magnetic field values extracted.

Alternatively in case plural rows of sensing elements are selected (activated) at once the biasing element may be controlled to apply a differently modulated bias voltage to each of the associated first conductive lines. The measured photocurrent in a read-out lines then contains contributions of magnetic sensing elements of plural rows but each contribution is modulated differently and can be separately extracted using at least one lock-in amplifier, or equipment for analog to digital conversion and subsequent FFT analysis such as e.g. a spectrum analyzer.

The at least one microwave source may be one or more RF antennas. The at least one microwave source may be controlled while irradiating to sweep frequency within a predetermined frequency range. The at least one microwave source may be configured to irradiate the magnetic sensing elements directly. Alternatively, a set of parallel microwave conductive lines may be provided for carrying a microwave signal generated by the at least one microwave source, the microwave lines being formed above the first and/or second contacts, and being electrically insulated from the first and second contacts and from the substrate. The microwave conductive lines may be positioned such that they at least partially cover portions of the substrate that are not covered by the first and or second contacts. In particular the microwave conductive lines may be configured to maximize coverage of the substrate portions uncovered by the first and/or second contacts to thereby maximize coupling in of microwaves into the diamond material.

In an embodiment of the invention the microwave lines are alternatingly connected to ground such as to define a set of coplanar microwave strips or a set of coplanar waveguides. In another embodiment there are dedicated ground electrodes, e.g. each connecting some of the second contacts, provided in-between the microwave lines, so as to obtain a coplanar waveguide structure without the need to alternate the microwave lines with microwave ground lines.

In a further embodiment of the invention the set of parallel microwave conductive lines are oriented parallel to the second conductive lines. Referring back to the matrix example here above this would mean that the microwave lines are parallel to the read-out lines, or in other words the columns of magnetic sensing elements.

In yet a further embodiment the at least one microwave source may be controlled to generate a modulated microwave signal.

In another embodiment of the invention the first contacts and second contacts are formed on the same surface of the substrate and the light generated by the at least one light source is directed to an opposite surface such as to illuminate the selected sensing elements. This is advantageous as the light is then not shielded by the contacts hence increasing the exposed surface and/or volume of the substrate.

The illumination, independent of the surface where it is incident upon, may be continuous across the predetermined area. Alternatively, the illumination is spatially varied across the predetermined area. Spatial variation may be obtained by mechanically displacing the light source, or by using one or more reflective elements such as at least one mirror, e.g. a polygon mirror, or by using at least one diffractive element, or by using multiple light sources that can be selectively addressed. In particular, the at least one light source may be a focused laser beam, or a line-shaped laser beam, or a 1-dimensional or two-dimensional array of LEDs or lasers such as e.g. Vertical Cavity Surface emitting lasers (VCSELs).

In a further embodiment of the present invention the measurement unit is configured to extract from the measured photocurrent sensed temperature values for each sensing element of the selected sensing elements.

In another aspect of the invention a method is provided for determining the magnetic field distribution in an area using a magnetic field sensing device comprising a predetermined area of a diamond NV center substrate, the predetermined area having a plurality of sensing elements, each of said plurality of sensing elements having a first contact and a second contact electrically contacting a surface of the diamond NV center substrate, said second contact being electrically isolated from said first contact; the method comprising the steps of:

The method also comprises placing the object for which the magnetic field distribution has to be determined in the proximity of the sensing elements, preferably at a defined distance of the sensing elements. Then the sensed magnetic field values are used to compute the magnetic field distribution, as known in the art.

Said object to be measured can be of any type and in any technical field. For example, the method of the invention can be used for bio-detection or biosensing within samples of various shapes, size or containers. The high sensitivity reached thanks to the method of the invention can for example allow to determine the magnetic field distribution within microfluidic devices, on chips or wafers, to monitor functioning of electronic systems, like detecting small currents on an integrated circuit. It can also be used for static measurements for quality control in a production context for example.

The figures are made for illustrative purposes and members may not have correct proportions to each other.

List of reference numbers used:

Examples of the invention will now be described in more detail with reference to the drawings.

It will be understood that, although the terms “first,” “second,” etc., may be used herein to describe various elements, components, regions, layers, and/or sections, these elements, components, regions, layers, and/or sections should not be limited by these terms. These terms are used to distinguish one element, component, region, layer, or section from another element, component, region, layer, or section. Thus, a first element, component, region, layer, or section discussed below could be termed a second element, component, region, layer, or section, without departing from the spirit and scope of the inventive concept.

The terminology used herein is for the purpose of describing particular embodiments and is not intended to be limiting of the inventive concept. As used herein, the singular forms “a” and “an” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “include,” “including,” “comprises,” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. Expressions such as “at least one of,” when preceding a list of elements, modify the entire list of elements and do not modify the individual elements of the list. Further, the use of “may” when describing embodiments of the inventive concept refers to “one or more embodiments of the present invention.”

It will be understood that when an element is referred to as being “connected to” or “coupled to” another element, it can be directly connected to or coupled to the other element, or one or more intervening elements may be present. When an element is referred to as being “directly connected to,” or “directly coupled to,” another element, there are no intervening elements present.

As used herein, the terms “substantially,” “about,” and similar terms are used as terms of approximation and not as terms of degree, and are intended to account for the inherent variations in measured or calculated values that would be recognized by those of ordinary skill in the art.

As used herein, the terms “use,” “using,” and “used” may be considered synonymous with the terms “utilize,” “utilizing,” and “utilized,” respectively.

illustrates a magnetic field sensing device comprising a predetermined area of a diamond NV center substrate () shown in the x-y plane, the predetermined area having a plurality of sensing elements, each of said plurality of sensing elements having a first contact () and a second contact () electrically contacting a surface of the diamond NV center substrate (), said second contact () being electrically isolated from said first contact ().

The diamond NV center substrate () is a diamond material containing Nitrogen Vacancy (NV) centers in the form of a thin plate having a surface area (in the x-y plane) typically in the range from 4 mm by 4 mm till 10 mm by 10 mm, and a thickness typically in the range from 100 μm to 500 μm.

The second or read-out contact () of each of the magnetic sensing elements is located inward to its first or bias contact (). In operation a bias voltage will be applied between the bias contact () and the read-out contact () of a sensing element and thereby create an electrical field in the substrate volume () of that sensing element. Hence adequately positioning and defining the contacts contributes to maximizing the sensing area () as well as the uniformity of the electrical field in the sensing area of the magnetic sensing element.

The plurality of sensing elements of the magnetic sensing device as exemplified inare arranged in a 2D array such as to define aby 3 matrix or grid of magnetic sensing elements forming the magnetic sensing device. Although aby 3 matrix is used as example, other configurations may be chosen dependent on the shape and geometry of the area to be sensed such as e.g. a matrix of sensing elements selected from a range of dimensions comprising 1×2, 2×2, 5×5, 5×10, 1×10, 5×1, 10×10, 100×100, 1000×1000.

Parallel conductive biasing lines () horizontally oriented connect the bias contacts () of rows of magnetic sensing elements. Parallel conductive read-out lines () vertically oriented connect the read-out contacts () of columns of magnetic sensing elements.

The width of the contacts and the conductive lines is typically in the range from 1 μm to 10 μm, while the thickness may typically range from 0.1 μm to 1 μm. The closest distance between a bias contact and a read-out contact of a same magnetic sensing element is typically in the range from 5 μm to 100 μm. The distance or pitch between read-out contact of adjacent magnetic sensing elements is an indication for the maximum resolution and is typically in the range from 10 μm to 200 μm.

A set of parallel microwave conductive lines () is provided for carrying a microwave signal. The microwave lines are formed using known techniques as used in semiconductor processing and manufacturing of integrated circuits and MEMS devices. The microwave lines are positioned above (in the z direction) the bias and read-out contacts () () and the bias and read-out lines () (), and are electrically insulated therefrom and from the substrate. The microwave conductive lines are positioned such that they at least partially cover portions of the substrate that are not covered by the bias and read-out contacts. In particular the microwave conductive lines may be configured to maximize coverage of the substrate portions uncovered by the bias and read-out contacts to thereby maximize coupling in of microwaves into the diamond material. The set of parallel microwave conductive lines () is oriented parallel to the read-out lines (), or in other words the columns of magnetic sensing elements.

To enable a magnetic sensing element to sense a magnetic field simultaneously a local electrical field is to be generated, the sensing element must be exposed to light of a predetermined wavelength or wavelength range, the magnetic element is to be irradiated with microwaves of a predetermined frequency or frequency range, and the photocurrent generated is to be collected and measured allowing to extract sensed magnetic field values therefrom. This can be enabled as follows:

The sensor described in the present invention can thus also be used as a temperature sensor array, or as a combined magnetic field and temperature sensor array.

As illustrated ina controller () is connected to a biasing element (), a read-out line selection unit () of a measurement unit, a microwave source () and a microwave line selection unit (). The biasing element () is connected to each row of bias contacts () via the associated bias line (). The microwave source (generator) () is connected to the microwave lines () via the microwave line selection unit. The read-out lines () are connected to the read-out line selection unit (). In an operational mode, the controller () is configured to control

The read-out procedure for the matrix of magnetic sensing elements can be as follows:

Apply a bias voltage to a selected one of the biasing lines. At the same time the other biasing lines may be connected to ground.

Illuminate at least the sensing areas () of the selected magnetic sensing elements (in this example the sensing elements of the selected row or in other words the sensing elements associated with the selected biasing line ()) with light of the appropriate wavelength or wavelength band.